1. Field of the Invention
The present invention relates to an expansion valve that constitutes a refrigerating cycle.
2. Description of the Prior Art
Although there are various types of expansion valve, widely used is an expansion valve in which a valve element is disposed, from the upstream side, opposite to an orifice which is formed by narrowing a high-pressure cooling medium passage, through which a high-pressure cooling medium to be fed into an evaporator flows, and the valve element is caused to perform opening and closing operation in response to the temperature and pressure of a low-pressure cooling medium discharged from the evaporator.
An expansion valve of this type can be used in a refrigerating cycle 1 in an air conditioner or the like of an automobile, as shown in FIG. 11. This refrigerating cycle 1 is composed of a cooling medium compressor 2 driven by an engine, a condenser 3 connected to the cooling medium compressor 2 on the discharge side thereof, a receiver 4 connected to the condenser 3, and an expansion valve 5 that causes the liquid-phase cooling medium from the receiver 4 to expand adiabatically so as to convert it into a gas-liquid two-phase cooling medium, and an evaporator 6 connected to the expansion valve 5. The expansion valve 5 is positioned within the refrigerating cycle 1.
The expansion valve 5 is provided with a high-pressure side passage 5b, through which the liquid-phase cooling medium flows into the valve body 5a, and a low-pressure side passage 5c, through which the gas-liquid two-phase cooling medium that has adiabatically expanded flows out. The high-pressure side passage 5b and low-pressure side passage 5 communicate with each other via an orifice 7. Furthermore, the expansion valve 5 is provided, in a valve chamber 8d thereof, with a valve element 8 that adjusts the volume of the cooling medium passing through the orifice 7.
A low-pressure cooling medium passage 5d pierces through the valve body 5a of the expansion valve 5. Furthermore, a plunger 9a is slidably disposed within this low-pressure cooling medium passage 5d. This plunger 9a is driven by a temperature-sensing drive section 9 fixed to the upper part of the valve body 5a. The interior of this temperature-sensing drive section 9 is divided by a diaphragm 9d so that an upper airtight chamber 9c and a lower airtight chamber 9cxe2x80x2 are formed in the temperature-sensing drive section 9. A disk portion 9e at the top end of the plunger 9a abuts against the diaphragm 9d. 
Furthermore, a compression coil spring 8a, which presses the valve element 8 via a support member 8c in the valve closing direction, is disposed within the valve chamber 8d in the lower part of the valve body 5a. This valve chamber 8d is blocked by an adjusting screw 8b screwed into the valve body 5a and is held in an airtight condition by an O-ring 8e. 
Also, an operating rod 9b that moves in the valve opening direction by the sliding action of a plunger 9a abuts against the bottom end of the plunger 9a. 
And the plunger 9a in the temperature-sensing drive section 9 transmits the temperature in the low-temperature cooling medium passage 5d to the upper airtight chamber 9c. The pressure of the upper airtight chamber 9c changes in response to the transmitted temperature. For example, when the temperature transmitted to the upper airtight chamber 9c is high, the pressure of the upper airtight chamber 9c increases so that the diagram 9d pushes the plunger 9a down. As a result, the valve element 8 moves in the valve opening direction so that the volume of the cooling medium passing through the orifice 7 increases, whereby the temperature of the evaporator 6 is lowered.
On the other hand, when the temperature transmitted to the upper airtight chamber 9c is low, the pressure of the upper airtight chamber 9c drops, the force for pushing the plunger 9a down by means of the diagram 9d becomes weak, and the valve element 8 moves in the valve closing direction due to the action of the compression coil spring 8a, which presses the valve element 8 in the valve closing direction, with the result that the volume of the cooling medium passing through the orifice 7 decreases and that the temperature of the evaporator 6 is raised.
In this manner, according to the temperature change in the low-pressure cooling medium passage 5d, the expansion valve 5 moves the valve element 8 to change the opening area of the orifice 7 and adjust the volume of the cooling medium passing through the orifice 7, thereby adjusting the temperature of the evaporator.
And in the expansion valve 5 of this type, the relationship between the temperature in the low-pressure cooling medium passage 5d and the opening area of the orifice 7 which causes the liquid-phase cooling medium to expand adiabatically so as to convert it into a gas-liquid two-phase cooling medium can be set by adjusting the spring load of the compression coil spring 8a which presses the valve element 8 in the valve closing direction, by adjusting the screw-in amount of the adjusting screw 8b. 
However, pressure fluctuations in the high-pressure cooling medium fed into the expansion valve may sometimes occur on the upstream side in the refrigerating cycle, and these pressure fluctuations are transmitted to the expansion valve with the high-pressure cooling medium liquid serving as a medium.
Then, in a conventional expansion valve as described above, when the cooling medium pressure on the upstream side is transmitted to the valve element by pressure fluctuations, the pressure fluctuations may sometimes pose the problem that the operation of the valve element become unstable. In this case, the flow control of the expansion valve is not accurately performed. Or this may sometimes cause the irregularity that the vibration of the valve element produces noise.
As a measure to solve this problem, there has been proposed a technique in which a spring gives an urging force sideways to a rod which is disposed so as to freely move forward and backward in an axial direction between a power element and a valve element so that an operation is stabilized (see Japanese Patent Application Laid-Open No. 2001-141335).
With the conventional technique mentioned above, however, although the purpose of coping with pressure fluctuations of a high-pressure cooling medium for stabilization of operation is achieved, the spring that pushes sideways the rod which moves forward and backward in an axial direction must be arranged in a stable condition, so that there is a fear of requiring high cost because of a complex structure and assembly work.
The object of the invention is to provide an expansion valve which enables stable operation against pressure fluctuations of a high-pressure cooling medium using simple and inexpensive means.
In order to achieve the above-described object, the expansion valve of the present invention comprises a valve body which has an orifice that provides communication between a high-pressure side passage through which a cooling medium flows in and a low-pressure side passage through which the cooling medium flows out; a valve element that adjusts the volume of the cooling medium flowing through the orifice; an operating rod that operates the valve element in the valve opening direction; and a temperature-sensing drive section that drives the operating rod. This expansion valve further comprises constraining means for constraining the above-described valve element or for constraining support member that is integral with this valve element, which is disposed on the upstream side of the orifice of the high-pressure side passage.
In this constraining means it is possible to adopt the following embodiments:
The constraining means is attached to the above-described valve body.
The constraining means gives a constraining force to the valve element by an elastic force.
The valve element is formed in the shape of a ball, and the constraining means is a support ring that supports the valve element.
The support ring comprises an elastically deformable, annular ring-shaped portion and a vibration-isolating spring. The vibration-isolating spring supports the valve element.
As the expansion valve of the present invention comprises the above-described components, by disposing constraining means of simple structure for constraining the valve element or valve-element support member, on the upstream side of the orifice, it is possible to suppress the vibration of the valve element caused by pressure fluctuations of the cooling medium on the upstream side of the refrigerating cycle.